Accelerometers can be found in electronic devices such as handheld video game devices, cellular telephones, pedometers, and portable medical devices. An accelerometer could be used to detect environmental conditions such as vibration, impact, or user activity. An accelerometer could also be used as a control device. For example, some video game devices and controllers incorporate accelerometers (and/or other sensors) that detect motion, orientation, or acceleration, where the detected phenomena can be translated into commands or instructions for the video game. A medical device might utilize one accelerometer to measure physical activity levels of the user and another accelerometer to detect physical impacts or trauma suffered by the medical device. For example, if an onboard accelerometer detects a relatively high physical impact, then the medical device could record the impact event and/or remind the user to inspect the medical device for proper operation.
In a medical device, human activity is typically characterized by relatively low frequency and relatively low amplitude excitation. In contrast, physical impacts are usually associated with relatively high frequency and relatively high amplitude excitation. Furthermore, both excitation modes can be associated with acceleration in any direction and at random or unpredictable times. At this time, no commercially available accelerometer device can effectively handle both excitation modes in a physically small, cost-effective, direction insensitive, and power efficient package.